Cathode-ray deflection circuit



March 26, 1957 G, Q FORBES 2,786,961

GATHoDE-RAY DEFLECTION cIRcuIT Filed July 24, 1952 v JNVENTOR. @new/v o.Fon-'355.5 Y

HND

CATHODE-RAY DEFLECTION CIRCUIT Gordon Donald Forbes, Sudbury, Mass.

Application July 24, 1952, Serial No. 300,581

6 Claims. (Cl. 315-24) This invention relates to an improved cathode-raydeilection circuit for imparting a radial displacement to a curve sweepon a cathode-ray tube screen.

It is a well-known expedient in the prior art that where it is desirableto obtain a long time base in a cathoderay tube presentation, to employa circular or spiral sweep if two constant amplitude sine wave inputvoltages are applied to the vertical and horizontal sweep voltage inputsof a cathode-ray oscillograph and the sine wave inputs vary in phase byninety degrees with respect to each other, the cathode-ray beam willtrace a circular pattern on the cathode-ray tube screen. By modulatingthe sweep voltages by a signal voltage the circular trace will beradially deflected to depict the signal desired to be presented. lf thesine wave input voltages, in addition to being ninety degrees shifted inphase with respect to each other, are applied as a damped wave trainincreasing frorn zero to a maximum amplitude or vice versa, a spiralsweep of the cathode-ray beam will be accomplished, in one case thespiral trace having its origin at the center of the tube and in theother case having its origin at the periphery of the tube screen. Ingeneral it is, therefore, necessary in order to develop a curvedcathode-ray tube sweep, to employ an oscillator for the purpose ofgenerating the sweep voltages, the output of the oscillator beingdivided into two inputs, one of the inputs being passed through a phaseshifting network to shift its phase ninety degrees with respect to theother input voltage and these sweep voltages if of constant amplitudecan then be applied to the cathode-ray tube to produce a circular tracewhich may be modulated radially to present the signals to be indicated.Similarly if a noncircular trace is desired, an oscillator capable ofhaving a damped sine wave train output is employed in lieu of constantamplitude oscillations and in this case a spiral trace will be generatedas described above. By varying the relationship of the amplitudes of theinput sweep voltages, it is possible to obtain other types of curvedsweeps, such as elliptical sweeps, as may be desired. The method ofgenerating these types of sweep voltages is already well-known in theart and will not be described in conjunction with the present invention.

Sine wave sweep voltages of constant amplitude or suitable damped trainsof input voltage waves will be assumed to be available for use withrespect to the inven tion and with the phase of one of the inputsshifted by ninety degrees with respect to the other input sweep voltage.

Previous radial modulation systems employed in conjunction withcircular, or other type, curved sweep cathode-ray presentations havegenerally employed a pushpull transformer for dividing the respectiveinput sweep voltages into two voltages, 180 degrees apart in phase,which are applied for example to the vertical deflection plates of thecathode-ray tube and a similar means has been employed for developingthe requisite voltages for the horizontal deflection plane. In anothertype of cirited States Patent i ice cuitry multigrid tubes have beenemployed, or an electrode placed at the center of the cathode-ray screenhas been employed. These older known systems have suffered seriousdisadvantages in that the radial deflection sensitivity is inverselyproportional to the distance Y from the center of the screen and as Wellwith lesser disadvantages such as considerable added expense. Where aspiral sweep is generated by the use of damped wave trains as abovebrieily described, the transformer used to couple the sweep voltages toampliliers connected to the respective deection plates has made itdifficult to obtain the necessary transient response to the damped wavetrains except where very special and expensive transformers areemployed. Where multigrid tubes are used it is almost impossible torealize the high order of balance required over appreciable deflectionsWith the result that the beam trace is distorted and may bend back uponitself, cross over and even double up into loops. Diculty is alsoencountered where multigrid tubes are employed because of drift due tothe continually varying ratio of plate to screen grid current. Thismeans that balanced conditions over even small ranges ofamplitude cannot be maintained over a reasonable period of time. For this reason evencarefully selected multigrid tubes are unsatisfactory. The use of anadditional electrode in the cathode-ray tube is also prohibitive from acost standpoint.

In accordance with the present invention a simple means has been devisedemploying simple triode vacuum tubes to develop the necessary deectionvoltages for dellecting plates of the cathode-ray tubes which is low incost and avoids or minimizes the difhculties encountered with previouslyemployed circuits for accomplishing a curved sweep on a cathode-ray tubescreen. In accordance with the present invention two input sweepvoltages diiering in phase by ninety degrees are applied respectively tothe grids of a pair of triode vacuum tubes. Each of these tubes hascoupled therewith an amplier tube connected in the plate circuit of theinput tube and a second amplier tube connected to the cathode of theinput tube, with the plate circuits of the amplier tubes respectivelyconnected to an opposed pair of deilection plates in the cathode-raytube. Since the grid of one of the amplier tubes associated with eachrespective input tube has its grid connected in the plate circuit, whilethe other amplier tube has its grid connected as a cathode follower,voltage outputs of the amplifier tubes are always one hundred eightydegrees out of phase with respect to each other. Two pairs of voltagesthus differing one hundredeighty degrees in phase with respect to eachother and ninety degrees between each of the pairs of voltages isavailable for applying to the deflection plates of the cathode-raytubeto provide the necessary curved sweep which may be either circularor spiral depending upon the nature of the amplitudes of the input sweepvoltages. The invention further employs a common source of potential forthe plates of all of the amplifier tubes and the cathodes of all of theamplifier tubes are coupled together in series with a common biasresistor to provide a definite bias voltage above the ground so that aninput signal to be displayed on the cathoderay tube can be appliedacross the common ground resistor to modulate the resultant of the sweepvoltages at any instance to cause Va radial deflection of thecathode-ray beam trace. Other features of the invention will becomeapparent by reference to the accompanying drawing and to the detaileddescription hereinafter given.

In the circuit illustrated in the drawing'a curved trace which may becircular, spiral,V elliptical or otherwise as desired, is applied to thescreen of the cathode-ray tube l0. The cathode-ray tube 10 is providedwith horizontal deflecting plates 11 and 12 and vertical 'decctingplates 13 and 14 to which the sweep voltages are applied to cause thedesired curved beam trace. Input signals which may be sine waves ofconstant amplitude or damped trains of sine wave voltages are applied tothe input sweep voltage terminals of the circuit. The input voltagesnecessarily are presumed to be supplied with a shift in phase of one ofthe voltages by ninety degrees with respect to the other voltages andany suitable well-known source for deriving such sweep voltages may beemployed.

The input sweep voltages may have their parameters so chosen that theamplitude of the sweep voltages may be constant or may vary in a knownpredetermined manner to give the type of curve sweep desired such ascircular, elliptical, spiral or other shapes.

The respective input sweep voltages applied to terminals 1S and 16 areapplied by means of conductors la and l@ to the grids Z and 21 of thetriodc vacuum tub-cs and 23, respectively. The plate 2S of the tube 22is suitablil connected by means of a suitable load resistance to asource of plate potential, and the plate is also capacitatively coupledto the grid of an amplier tube 211. which has its plate 25 connected tothe source of plate current and capacitatively coupled to the verticaldeilection plate 13 of .the cathode-ray tube 1t). The iirst input tube22 has its cathode connected by means of a suitable biasing resistor toground which is the return side of high voltage source of plate current.The second amplifier tube 26 has its grid connected as a cathodefollower to the cathode of the tube 22 and has its plate 27 connected tothe source of plate potential and capacitatively coupled to the oppositevertical deection plate 14 of the cathoderay tube 10.

The tubes 24 and 26, respectively, serve as amplier tubes and thevoltage on the grid of tube 24 will also be a hundred eighty degrees outof phase with respect to the sweep voltage appearing on the grid 20 ofthe tube 22, while the voltage on the grid of amplifier tube 26 will bein phase with the voltage on the grid of input tube 22 and accordinglythe plate voltages of the amplier tubes 24 and 26 and the voltagesappearing at the vertical deflection plates 13 and 14 will be onehundred eighty degrees out of phase with respect to each other which isdesired for proper operation of the cathode-ray tube.

Similarly, the vacuum tube 23 connected to the second input sweepvoltage at terminal 16 has its plate 29 connected to the common sourceof plate voltage and also capacitatively coupled to the grids of thethird amplier tube 30 which has its plate circuit 31 connected to thecommon source of plate voltages and capacitatively coupled to thehorizontal deilection plate 11 of the cathode-ray tube 10. Similar tothe tube 22, the second input tube 23 has its cathode connected toground across suitable bias resistors and also capacitatively coupled tothe grid of the fourth amplifier tube 32, which similarly has its platecircuit 33 connected to the common source of plate potential and to thesecond horizontal deflection plate 12 of the cathode-ray tube 10. Thevoltages appearing on the grids of tubes 30 and 32 and on the horizontaldeflection plates 11 and 12 of the cathode-ray tube will respectively be180 degrees out of phase with respect to each other Ifor the samereasons described above with respect to the input tube 22; and alsothese voltages will have been ninety degrees out of phase, respectively,with the voltages appearing on the vertical deflection plates 13 and 14due to the fact that the input sweep voltage applied to terminal 16 isninety degrees shifted in phase with respect to the input voltageapplied to the input terminal 15. As will be noted in the drawing theplate circuit of all of the tubes are connected in common throughsuitable load resistors to a single source of plate potential and inaddition capacitors 34 and 35 connected across the plate Outputs oftubes 22 and 23 are provided to reduce any grid cathode coupling whichmight otherwise unbalance the system.

In the circuit as so far described it will be understood that if twoinput sweep voltages differing in phase with respect to each other byninety degrees are applied, the input sweep voltages at the respectiveinput terminals l5 and 16 will cause the tubes 22 and 23 to conduct andapply corresponding signal voltages to the grids of amplier tubes 24 and26, which voltages will be 180 degrees out of phase with respect to`each other due to the fac that the grid of tube 24 is connected in theplate circuit of tube 22 while the grid of tube 26 is coupled to thecathode of tube 22. The voltages appearing in the plate circuits ot theamplier tubes 24 and 26 will accordingly appear across the Verticaldeilection plates 13 and 14 of the cathode-ray tube. In a similar mannerthe phase shifted input sweep voltage applied to the terminal 16 willcause tube 23 to conduct, the plate and cathode outputs of Which areapplied to the grids of amplifier tubes Eil and 32, respectively, toproduce a pair of output voltages differing in phase with respect toeach other by a hundred eighty degrees and being further ninety degreesshifted one hundred eighty degrees out of phase with respect to eachother and which are applied from the plate circuits of these ampliertubes to the horizontal deilection plates 11 and 12 of the cathode-raytube 1t?, the voltages on the plates 11 and 12 being further shiftedninety degrees in phase with respect to the voltages appearing on plates13 and 14.

if the input sweep voltages are constant amplitude sine Waves shiftedninety degrees in phase with respect to each other, the cathode-ray tubebeam will trace out a circle on the screen of the cathode-ray tube 10,the radius of the circle being dependent upon the level of the constantamplitude input sweep voltages. If the inputsweep voltages, in additionto being shifted by ninety' degrees,

comprise trains of damped sine waves the beam trace will be a spiralhaving its origin either at the center or the periphery of the screen ofthe cathode-ray tube l@ depending upon whether the amplitude of the wavetrains starts at a minimum or zero and increases to a maximum, or startsat a maximum and decreases toward zero, respectively. It will thus beseen that a curved trace on a cathode-ray tube screen can beaccomplished by means of the circuit so far described without it beingnecessary to employ any special designed transformers or multigrid tubesand thus avoiding the ditiiculties encountered in the prior artconstructions in this regard.

It will be noted that the cathodes of all of the amplifier tubes 24, 26,30 and 32 are connected in common across a common bias resistor 3S toground which thus maintains the cathodes at a desired bias voltage aboveground and across the common cathode on resistor 38 there are connecteda pair of input signal terminals 36 and 37 to which can be applied thecurve detlecting signal which it is desired to display on thecathode-ray tube. The curve dellecting signal will vary the bias voltageon the cathodes of the amplifier tubes and will accordingly cause avariation in the instant resultant sweep voltages applied to thecathode-ray tube 10 to cause a radial deviation in the cathode-ray tubebeam trace, which will thus make the desired `signal visible on thecathode-ray screen with an amplilied time base due to the curved traceof the beam. This means of modulating the sweep voltages does notinvolve any complications which would otherwise be introduced if themodulation were to be applied through the sweep voltage input circuits.

Having described a preferred embodiment of my invention I wish it to beunderstood that the circuit illustrated may be modied and equivalentelements substituted therefor without departing from the scope of theinvention as defined in the appended claims.

I claim:

l. An improved circuit for imparting a radial displacement to a curvedsweep of a cathode-ray tube beam, comprising a cathode-ray tube havingtwo pairs of electron beam deflecting plates, a pair of circuit inputterminals adapted to have respective input sweep voltages appliedthereto with one of the input voltages shifted ninety degrees in phasewith respect to -the other input voltage, a pair of input triode vacuumtubes each having its grid connected to a respective one of said inputterminals, a pair of amplifier tubes connected in the output circuit ofeach respective input tube to provide four amplifier tubes with theircathode electrodes joined to each other and applied to ground through acommon bias resistor across which may be applied a modulating signalaltering the cathode-ray tube presentation and one of said pair ofamplifier tubes having its grid coupled to the plate of the associatedinput tube and the grid of the other amplifier tube of said pair ofamplifier tubes being connected to the cathode of the associated inputtube, the plates of each pair of amplifier tubes being connected torespective plates of one of the pairs of electron beam detiecting platesof the cathode-ray tube whereby each input sweep voltage is divided intoa pair of voltages diering in phase by one hundred eighty degrees whichvoltages are applied to the respective plates of one of the pairs ofdefiection plates of the cathode-ray tube and the voltages applied toone of the pairs of defiecting plates differing in phase by ninetydegrees with the corresponding voltages applied to the other pair ofdeflecting plates of the cathode-ray tube.

2. A cathode ray tube curved presentation radial defiector circuit,comprising a cathode ray tube plurality of cathode ray deflectingplates, a plurality of amplifiers corresponding in number to saidplurality of cathode ray deflecting plates and each of said plurality ofamplifiers having a cathode electrode connected directly to the cathodeelectrodes of the other of said amplifiers, a cathode bias resistorconnected in common between the cathode electrodes of all of saidamplifiers and ground, and modulating signal conducting means fordefiecting the cathode ray tube presentation by the application ofcathode ray tube modulating signal across said cathode bias resistor.

3. A cathode ray tube presentation modulating circuit, comprising acathode ray tube having two pairs of cathode ray deflection plates, afirst input tube having plate grid and cathode electrodes with means forimpressing an electrical input -at a predetermined phase on the grid `ofsaid first input tube, a second input tube having plate grid and cathodeelectrodes with means for mpressing on said second input tube grid asecond electrical input shifted in phase from the phase of the input tothe grid of the first input ltube, a separate grid actuated amplifiertube for each plate and for each cathode of said first and second inputtubes and each amplifier tube having grid and cathode electrodes and aplate electrode from which the amplifier tube output is passed to acathode ray deflecting plate of said cathode ray tube, and a commoncathode bias resistor between ground and the connected cathodes of saidamplifier tubes and modulating signal contact means whereby a cathoderay tube presentation may be deflected by applying a cathode ray tubepresentation deflecting signal thereto.

4. A cathode ray tube modulation circuit, comprising a cathode ray tubehaving two pairs of deflection plates, a first input tube having plategrid and cathode electrodes, a first input tube resistor between thecathode and the grid electrodes of said first input tube, a firstamplifier having `a grid capacitively coupled with the plate electrodeof said first input tube and having a plate capacitively :coupled with acathode ray tube first deflection plate and having a cathode, la secondamplifier having a grid capacitively coupled with the cathode of saidfirst input tube and having a plate capacitively coupled with a cathoderay tube second deflection plate and having a cathode, a second inputtube having plate grid and cathode electrodes, a second input tuberesistor between the cathode and the grid of said second input tube, athird amplifier having a grid capacitively coupled with the plate ofsaid second input tube and having a plate capacitively coupled with acathode ray tube third defiection plate and lhaving a cathode, a fourthamplifier having a grid capacitively coupled with the cathode of saidsecond input tube and having a plate capacitively coupled with a cathoderay tube fourth deflection plate and having a cathode, a common biasresistor connecting the cathodes of said four amplifiers to ground, anda modulating signal conductor referred to ground and connected to thejunction of the four amplifier tube cathode electrodes for modifying thecathode ray trace of said ycathode ray tube.

5 A radial modulator of a curved sweep on a cathode ray tube screen,comprising a cathode ray tube having a pair of vertical and a pair ofhorizontal cathode ray deflection plates, the radial modulatorcomprising a pair of signal input tubes receiving signal on the controlgrid of each tube and providing outputs from both the plate and from thecathode of each signal input tube, a first pair of amplifier -tubesprovided with plate grid and cathode electrodes and lassociated with oneof said input tubes by having a first amplifier tube grid capacitivelycoupled with the plate of a first signal input tube and by having afirst amplifier tube plate capacitively coupled with the first of a pairof vertical cathode ray defiection plates, and by having a secondamplifier tube grid capacitively coupled with the cathode of the firstsignal input tube and the second amplifier tube plate capacitivelycoupled with the second of the pair of vertical cathode ray deflectionplates, and a second pair of amplifier tubes provided with plate gridand cathode electrodes and with a third amplifier tube grid capacitivelycoupled with the plate of a second signal input tube and with a fourthamplifier tube grid capacitively coupled with the cathode of the secondsignal input tube, Iand the two plates of said third and fourthamplifier tubes capacitively coupled with the pair of horizontal cathoderay defiection plates, and an amplifier cathode bias resistor biasing toground the four cathodes of the four amplifiers, Iand means for applyingacross the resistor biasing to ground the cathodes of said amplifiers amodulating signal for causing a radial defiection of a curved sweep onthe cathode ray tube screen.

6. The modulator in the above claim 5 wherein capacitors are connectedacross the plate outputs of the pair of signal input tubes to reduce anygrid-cathode coupling tending to unbalance the system.

Bobb May 21, 1947 Bryant May 31, 1949

